1. Field of the Invention
The present invention is related to construction field, specifically to the development of improved cementitious compositions as well as to the methods applied for the obtention.
2. Description of the Related Art
Portland cement is the main cement material of construction sector. It is the main element of union in concrete blocks, recovering for carpet tiles for floors, grout, wood fiber panels, mortars, glues for tiles, etc. In spite of its great applicability in construction field, Portland cement has some important disadvantages including low resistance to early compression force and a high contraction by drying; due to these circumstances, great efforts have been directed for the obtention of cementitious compositions with greater advantages than Portland cement allowing superior versatility in their applications.
Portland cement consists mainly of tricalcium silicate ((CaO)3 SiO2) with small amounts of dicalcium silicate ((CaO)2 SiO2), and it is obtained by burn from a stone mixture of calcium oxide and argillaceous material; due to the argillaceous component, Portland cement contains from 5 to 13% of tricalcium aluminate ((CaO)3 Al2O3). When this component is present in superior amounts, it causes an excessively fast setting of concrete or mortars, which is a problem when it is needed to transport from the mixed site to the place of its application. To avoid this effect of express setting, the calcium sulphate inclusion is well-known (CaSO4) using plaster in cement by the joint milling with Portland clinker.
However, the calcium sulphate presence causes two important undesirable effects in cement compositions. One of them is the plaster of Paris formation, which is occurring by the partial dehydration of plaster by the heat generated during the milling process (formula 1):CaSO4.2H2O→CaSO4.½H2O+1½H2O  Formula 1.
This component hardens the mixture and interferes with handling operations such as transportation, packing and concrete appearance.
Although it has been described that hydrated mixtures of hemi-hydrate calcium sulphate and Portland cement can be beneficial by its use in cement compositions1, it has been observed chemical reactions between sulphate ions (provided mainly by calcium sulphate) and aluminum compositions contained in the hydrated Portland cement, generating a crystalline calcium sulfoaluminate hydrate of great volume called ettringite2,3 (3CaO.Al2O3.CaSO4.32H2O). Ettringite results from the reaction of hydration of tricalcium aluminate present in Portland cement with sulphate (see formula 2), which increases the volume of concrete, causing its breaking, cracking and crushing by the increase of expansive forces present in cement. At this time, ettringite is considered as an important factor in concrete deterioration in medium and long term.(CaO)3Al2O3+CaSO4+32H2O→3CaO.Al2O3.CaSO4.32H2O  Formula 2.
Although mixtures of Portland cement and calcined plaster have been used previously and in some cases they have been advantageous, interaction between tricalcium aluminate and sulphate forming ettringite has limited greatly the use of such mixtures. For example, the attempts to improve the resistance to water in plaster boards mixing Portland cement and calcined plaster have been of limited success due to ettringite formation. Due to these circumstances, plaster and Portland cement mixtures have been directed mainly as “fast solutions”, that are known of poor durability in the long term.
The formation of ettringite in Portland cements with a high content of tricalcium aluminate may cause severe problems, which needs higher proportions of plaster to delay this effect.
Multiple developments have been centered in inhibiting or controlling the formation of plaster of Paris and/or ettringite in cement compositions, such as those in which the amount of tricalcium aluminate is varied4 those were the type of present components prevent the ettringite formation5,6 and those in where diverse types of calcium sulphate are mixed with other components1,7. In general, with these developments, compositions have been obtained and those can be used with water or another component to produce fluid mixtures, with a less demand of water, greater initial compression force resistance and low alkali functionality8.
Nevertheless these compositions have a series of disadvantages, as much in their procedures for manufacture as in their characteristics, such as:
a) High cost,
b) Low resistance to compression force,
c) Longer times of setting,
d) Resistance to early compression forces comparable to those of ordinary Portland cements, and
e) The inclusion of greater number of elements in the composition, which makes difficult to obtain homogenous mixtures and increases the amount of energy used for its milling.
Due to these circumstances, the development of cheaper cementitious compositions is convenient, getting similar chemical and physical characteristics of Portland cement, including a suitable resistance to final compression force and a lower susceptibility to crack and crumble. Also it's desirable that improved compositions manage or eliminate ettringite formation, improving resistance to compression force.